Some smoke detectors may be providing homeowners with a false sense of security. Most homeowners aren't aware of the problem. A number of homeowners had the same problem; smoke alarms were going off for no reason. They would find that the battery inside had expanded, cracked, or blown up. The homeowners had First Alert-BRK model 4120b or 4120sb smoke alarms and had been using Duracell batteries.

First alert admits these smoke alarms are only compatible with Eveready or Energizer batteries. Other batteries can bulge and explode inside the smoke alarms causing them to go off, possibly not work at all, or prompt homeowners to shut off the alarms entirely. The First Alert smoke alarms in question were manufactured before October 2000.

DENVER (CBS4) Some smoke detectors may be providing Colorado homeowners with a false sense of security. A CBS4 investigation has found a flaw in a popular smoke detector that renders the detector useless in some situations. Most homeowners aren't aware of the problem.

Ginger Sayor figured there was something wrong with the smoke alarms in her Castle Pines home.

"They would go off in the middle of the night for no reason," Sayor said.

On a regular basis, the seven hard-wired smoke alarms in her home would go off, sending her husband up a ladder, only to find the back-up battery inside expanded or exploded.

"It's pretty dangerous -- they pop; its a pretty good explosion for a 9 volt battery," Tom Sayor said.

"You are sitting there with a sense of complacency every time the alarm goes off you're not thinking about safety first, you're thinking about where is the battery so I can change it because you're annoyed, " Ginger Sayor said.

A mile away, Dave Grewe was having the same problems with his nine smoke alarms that were going off for no reason. He would find that the battery inside had expanded, cracked or blown up.

The annoyance made him take drastic measures.

"They are off right now and I've had to disable them because I cant get them to silence," Grewe said.

When we began investigating, we found these were more than just isolated problems.

Both homeowners had First Alert-BRK model 4120b or 4120sb smoke alarms and had been using Duracell batteries.

First alert admits these smoke alarms are only compatible with eveready or energizer batteries.

Other batteries can bulge, and explode inside the smoke alarms causing them to go off, possibly not work at all, or prompt homeowners to shut off the alarms entirely.

Smoke alarms are credited with reducing home fire deaths by 50 percent.

First Alert says the primary reason they don't go off in a fire death is due to missing, disconnected or dead batteries.

The South Metro Fire Rescue Department joined CBS4's investigation of looking into how widespread the problem is.

"It's on a much larger scale than what we thought originally," said Amy Teddy of South Metro.

As they looked into the problems, Teddy found home after home with the same problems. Homeowners were using incompatible batteries with the First Alert alarms and it was leading to exploding batteries, malfunctioning detectors, false alarms and systems that just shut off.

"I'm now realizing the huge scale of this problem, and fortunately there haven't been any injuries, but we don't want to wait until there are injuries," Teddy said.

"Lets take the bull by the horns, cowboy up and make some people accountable, because this is not OK," she said.

The homeowners CBS4 contacted felt that the way they were finding out about the problem wasn't satisfactory. They said First Alert never notified them of what was going on.

"I think it's very annoying that we were not alerted sooner," Ginger Sayor said. "We have been here 6 years, and it's an unsafe and unreliable situation."

The First Alert smoke alarms in question were manufactured before October 2000.

Officials with the Consumer Product Safety Commission said they are aware of this problem. They said they have an active investigation into the matter and are asking consumers to contact them if they have the same problem. CPSC has not issued a recall.

South Metro Fire is now offering compatible batteries to people in their district with these types of smoke alarms.

The Models:

• First Alert • 4120B • 412OSB • Manufactured before October 2000

The Problem: • Replacement batteries other than those recommended can cause the unit to stop working. Recommended replacement batteries are the Energizer Max or Energizer 522 or Eveready 1222.